code: def test_cpu_amp_precision_context_manager():
      """Test to ensure that the context manager correctly is set to CPU + bfloat16."""
      plugin = MixedPrecision("bf16-mixed", "cpu")
      assert plugin.device == "cpu"
      assert plugin.scaler is None
      context_manager = plugin.autocast_context_manager()
      assert isinstance(context_manager, torch.autocast)
      assert context_manager.fast_dtype == torch.bfloat16
  
imports: import os
  import re
  from unittest import mock
  import pytest
  import torch
  from lightning.pytorch import Trainer
  from lightning.pytorch.demos.boring_classes import BoringModel
  from lightning.pytorch.plugins import MixedPrecision
  from torch import Tensor
  from tests_pytorch.helpers.runif import RunIf
label_desc: Use image node_id 4 for calling a global function with example usage: test_cpu_amp_precision_context_manager() without return types